I think that the SVS PB2000 and Rythmik LVX12 will have very similar outputs capabilities. Here is my thinking. SVS has said the the cylinder and box version of their subwoofers give you almost indistinguishable performance. They were designed that way in fact. The SVS PC2000 was recently measured on Audioholics (
http://www.audioholics.com/subwoofer...r/measurements ). As you can see from the long term outputs, the SVS sub can output about 105 dB before compression sets in. Unfortunately I don't have measurements for the Rythmik LVX12. But, the FV15HP was measured on Data-bass (
http://www.data-bass.com/data?page=system&id=51&mset=49 ). As you can see in either port configuration the Rythmik subwoofer can output about 110 dB before compression begins setting in. According to Rythmik's webpage (
http://www.rythmikaudio.com/products1.html ) the LVX12 is about 5.5 dB down from the FV15HP. The LVX12 has the same port tuning modes as the FV15HP, so pick a port configuration and imagine shifting those all down by about 5 dB and you should have a pretty good idea of what the LVX12 can do. This isn't going to be exact because the drivers are different sizes as are the boxes, etc. But, it should be pretty close. This means that the Rythmik LVX12 can output about 105 dB before compression sets in. Either the SVS PC2000 or Rythmik LVX12 can probably burst more than 105 dB if only asked to do so for a split second, but this is about as much as they can do continuously from 2 meters away without compression really beginning to set in.
So the two seem to be very similar in output capabilities. This means, to me, that the case for getting the Rythmik is a lot stronger. The Rythmik LVX12 offers port tuning capabilities and servo technology. Whereas the SVS PB2000 doesn't have either. On post 33 of this other thread (
http://forum.ascendacoustics.com/sho...5586#post55586 ), I mention where Dave F. (Ascend's owner and speaker designer) and Brian (Rythimk's owner and speaker designer) talk about the advantages of Rythmik's servo technology over just using DSP, like SVS and most other subwoofer companies implement.
Good luck. Hopefully this will help you decide which sub is best for you.